Apparatus for cutting off successive lengths of a continuously moving, elongate workpiece such as tubing emanating from a mill, is well known in the art. Typically, tube cutoff apparatus comprises a die set mounted on a carriage for selective acceleration along the length of the tubing. The die set and carriage are in turn mounted on a flying type ram which is operated in synchronism with the movement of the tubing. The die set includes a reciprocating severing blade operated by the ram for severing the clamped tubing as the die set and tubing move in unison. More recently, tube cutoff apparatus, such as that shown in U.S. Pat. No. 4,108,029, include a die set having a reciprocable notching blade for producing a stress relieving notch in the periphery of the tubing immediately prior to the severing operation.
The clamping jaws employed with the prior art tube cutoff apparatus of the type mentioned above typically employ a pair of reciprocable die jaws operated by the flying ram. These die jaws each comprise a pair of spaced apart clamping members stationarily mounted relative to each other and provided with clamping surfaces contoured to conformingly engage the sidewalls of the tubing. The clamping members include blade supporting surfaces spaced apart a distance marginally greater than the thickness of the severing blade; the severing blade passes between the blade supporting surfaces of the clamping members and is laterally supported by such surfaces so as to prevent blade deflection during the severing process. As shown in U.S. Pat. No. 3,924,502, the opposing faces of the clamping members may be provided with relieved steps or surface areas immediately adjacent the blade supporting surfaces and downstream in the stroke of the severing blade to provide additional clearance between the severing blade and the clamping members to accommodate the coined and compressed material being severed from the tubing. The cutoff apparatus of the type described above, although entirely suitable for most cutoff operations, is nevertheless subject to certain improvements as will be discussed below.
As previously indicated, the severing blade of prior art cutoff apparatus moves in a plane aligned with the path of travel of the notching blade. In some areas, the path of travel of the severing blade may not be precisely aligned with that of the notching blade, either due to wear over an extended period of use, or as a result of errors in original manufacturing tolerances. In the case of minor misalignment in the paths of travel of the notching and severing blades, the severing blade may initially engage the exterior sidewall of the tubing along the edge of the notch rather than penetrating the notch itself; as a result, inwardly directed stresses are placed on the sidewall of the tubing which may result in slight "dimpling" of a portion of the sidewall before the severing blade is deflected into the notch. This, of course, defeats the purpose of the notching blade since the distortion produced in the sidewalls by the dimples results in an inferior product suited for use in many applications.
Additionally, misalignment of the severing blade relative to the notching blade not only increases wear of the severing blade, but tends to produce additional drag on the severing blade, since such blade may frictionally engage the blade supporting surfaces of the clamping members. Additionally, misaligned severing blades tend to increase the amount of coined and formed tubing material which is drawn along with the blade as it is drawn out of the severed tube.
Heretofore, there has not been provision made for compensating for the effects of misalignment between the paths of travel of the notching and severing blade. The notching and severing blade have been of essentially equal thicknesses, and the opposing faces of the clamping members have been spaced apart a distance to closely receive and accommodate both blades.
Accordingly, it is an important object of the present invention to provide improved tube cutoff apparatus which eliminates each of the deficiencies inherent in prior art apparatus and yields satisfactory cutting quality in spite of minor misalignment of the cutting paths of the severing and notching blades.
Another object of the present invention is to provide tube cutoff apparatus with the type mentioned above in which the notching blade possesses a thickness greater than that of the severing blade so as to create a notch having an inherent tolerance sufficient to accommodate the path of travel of a severing blade not precisely aligned with the notch.
A still further object of the present invention is to provide tube cutoff apparatus as described above having improved die jaw clamping members adapted to receive the thicker notching blade, but yet which provides blade supporting surfaces for the severing blade to prevent deflection thereof during the severing operation.
Another object of the present invention is to provide improved die jaw clamping members of the type mentioned immediately above which provide clearance spaces between the members and the severing blade for receiving coined and formed material severed from the tube during the severing operation, thereby decreasing friction between the blade, the clamping members and the tubing, while improving the quality of the cut.
Another object of the invention is to provide cutoff apparatus as mentioned above which reduces the amount of drag or friction between the blade and the die jaws both on the forward and return stroke of the severing blade.
These and further objects of the invention will become clear or be made apparatus during the course of the following description of the invention.